PROPERTY, EQUIPMENT AND SOFTWARE, NET (Schedule of Property, Equipment and Software) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 245,142	$ 210,039
Less accumulated depreciation	(134,243)	(106,388)
Property, equipment and software, net	110,899	103,651	[1]
Capitalized website and internal-use software development costs
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	102,004	81,710
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	79,589	74,236
Computer equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	40,129	32,450
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	17,351	16,435
Telecommunication
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	4,554	3,996
Software
Property, Plant and Equipment [Line Items]
Property, equipment and software, gross	$ 1,515	$ 1,212

[1] As of January 1, 2018, the Company adopted Accounting Standards Update 2014-09, "Revenue from Contracts with Customers (Topic 606)" ("ASC 606"), using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.